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A STUDY OF THE BUCKLING DESIGN FOR PARTIALLY FILLED SPHERICAL TANKS

Unstiffened spherical tanks supported at the equator are used in LNG-carriers. From among numerous other load conditions, the buckling load induced by partial filling with LNG plays an important role in determining the thickness of the tank. In this case, the region of the tank close to and above the liquid surface is the most critical area in terms of buckling requirements. In this area there are biaxial stresses consisting of membrane compressive stress in one direction and tensile stress in the opposite direction. This paper describes experimental and theoretical studies of the buckling design of spherical tanks under biaxial stress conditions. The experiment on buckling was carried out with the use of an extension of Yao's theory to the plastic region. As a result of investigation of design criteria stipulated in API Standard and ASME Code, it became evident that design buckling load for tension-compression biaxial stress conditions is too conservative due to neglect of the effect of tensile stress. Consequently a buckling design chart for arbitrary biaxial stress conditions has been proposed using the method of linear correlation between standard buckling loads. To confirm the validity of the above method, theoretical buckling loads for rectangular plates under biaxial stresses were calculated by using Galerkin's method, and the error resulting from the linear correlation was discussed.

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